Yellowing & Spotted Leaves on a Potted Lemon Tree
Lemon trees (Citrus limon) dot the landscape in sunny yards across the country and line patios and balconies throughout U.S. Department of Agriculture plant hardiness zones 9 through 11. As potted plants, these sturdy trees are unrivaled beauties with few problems, so when spotted or solid yellow leaves appear, your lemon tree likely has only a minor problem with a simple solution.
Scale are problematic for plants both indoors and out. These tiny pests often resemble bumps, waxy growths or nonspecific mildews to the casual observer, delaying proper diagnosis and treatment. Scale feed directly on the liquid inside plant tissues, stressing affected lemons and causing a variety of responses. California red scale (Aonidiella aurantii) and yellow scale (A. citrina) feed on leaves, twigs, branches and fruits, causing leaves to turn partially or completely yellow and drop. Purple scale (Lepidosaphes beckii) feed on all parts of the lemon tree, sometimes resulting in yellow halos on affected leaves.
Armored scale like California red scale, yellow scale and purple scale can be more difficult to manage than their soft-shelled kin, but control is attainable. Narrow-range oil can be used to smother these immobile insects — it must be applied with care and never when the ambient temperature will be above 80 degrees Fahrenheit. More toxic chemicals like carbaryl, chlorpyrifos and methidathion can be applied with a permit from your county’s agricultural commissioner. Use these with caution since they can render your fruits unsafe to consume. The parasitic wasp Aphytis melinus has shown success in controlling California red scale and other armored scales but will be killed by any lingering broad-spectrum pesticide residue.
Several different mites feed on lemon tree foliage, leaving small yellow dots called stippling and causing leaves to develop yellow spots or turn entirely yellow from stress. Citrus red mite (Panonychus citri), sixspotted mite (Eotetranychus sexmaculatus), twospotted spider mite (Tetranychus urticae) and the Yuma spider mite (Eotetranychus yumensis) are the most common of these diminutive arachnids found on lemon, where they may spin tiny silken threads as they feed in clusters on the undersides of leaves. Using a hand magnifying glass can help you get a better view of the mites affecting your plant.
Mites are not insects, so broad-spectrum insecticides will not clear an infestation. In fact, broad-spectrum insecticides often make mite problems worse by killing off natural enemies that may be able to keep the population in check otherwise. Wettable sulfur sprays or narrow-range oils are often effective against mites and are considered safe for food crops. Miticides like acequinocyl, hexythiazox or pyridaben can be applied to lemons, but carefully observe the preharvest intervals for each individual chemical. Bifenazate and etoxazole are considered safe only for nonbearing lemon trees.
Phytophthora Root Rot
Although uncommon in lemons potted in sterilized soils, phytophthora root rot is present in many lemon groves, where plant materials may have been harvested prior to potting. This soil-borne fungus infects the root system of susceptible cultivars, destroying feeder roots and infecting the root cortex. Affected trees may develop yellow leaves that drop, depending on the severity of root damage. All lemon trees may be treated with mefenoxam or fosetyl-al, regardless of fruit production, but application rates and methods differ between bearing and nonbearing plants. As affected trees attempt to recover from this dangerous disease, provide supplemental water and small amounts of fertilizer daily or weekly to help the plant compensate for the nutrients lost to damaged roots.
Yellowing & Spotted Leaves on a Potted Lemon Tree. Lemon trees (Citrus limon) dot the landscape in sunny yards across the country and line patios and balconies throughout U.S. Department of Agriculture plant hardiness zones 9 through 11. As potted plants, these sturdy trees are unrivaled beauties with few …
What Causes Yellow Spots on Meyer Lemon Trees?
The Meyer lemon (Citrus x meyeri) is a small, decorative tree known not only for its orangey-yellow fruits but for its diminutive size and lustrous green foliage. Popular in container gardening, this small tree is also useful for small backyard gardens. The fruits are less acidic than most lemons, making them a favorite for cooking. In U.S. Department of Agriculture zones 9 through 11 they flourish outdoors, but in cooler climates they should be brought in before any danger of frost. Occasionally, yellow spots on the leaves or fruit will appear, and may be caused by environmental, insect or disease issues.
Yellow spots on leaves may be the result of insects sucking out juices from the foliage. Spider mites leave yellow stippling on leaves and often aren’t noticed right away. Scale insects look somewhat like shallow helmets, and often blend into bark. They also suck juices from leaves and fruits, leaving behind yellow spots. Stink bugs leave yellow stippling as well as brown spots, and emit a foul-smelling scent. All can be controlled with insecticidal soaps, and traps can be set for stink bugs. Read and follow pesticide label directions carefully.
Damage from Disease
Diseases that attack Meyer lemons are usually bacterial or fungal in nature. Citrus canker is an extremely contagious bacteria that causes circular yellow spots on leaves, fruits and twigs. Prevent infections with copper-based fungicides. Citrus scab is a fungal disease that often begins with yellow spots that quickly develop into scabby lesions. Greasy spot, another fungal disease, causes yellow to brown blisters. Prevent and control fungal diseases with a copper-based fungicide, carefully following label directions.
Irregular yellow spots on leaves with no definite edge may indicate a nutrient deficiency. Magnesium deficiency causes yellow splotches on the outer edges of leaves and is more common when soil pH drops below 5.0. Correct pH by adding lime to the soil until it measures between 6.0 and 8.0, which enables roots to access the available magnesium in the soil. Zinc deficiency causes yellow spots between the leaf’s veins and can be corrected with a foliar spray of zinc sulfate.
Although Meyer lemon trees are generally considered hardier than most citrus, they are only hardy to USDA zone 9 and may suffer cold damage in colder climates. Fruit may show light yellow spots that may be visible but are often difficult to detect. The spots later develop into pitted areas that affect the quality of the fruit. While there are a number of methods that professional citrus growers use to detect cold damage, home gardeners can detect injury with a simple black light, which highlights the damaged areas.
- University of Florida Nassau County Extension: Meyer Lemon
- NPR: The Meyer Lemon: More Than a Pretty Face
- ID Tools: Citrus Diseases
- Louisiana State University Ag Center: Louisiana Home Citrus Production
- University of Missouri Extension: Aphids, Scales and Mites on Home Garden and Landscape Plants
- Texas A&M University: Citrus
- Redwood Barn Nursery: Citrus: When Things Go Wrong
Lori Norris has been writing professionally since 1998, specializing in horticulture. She has written articles for the Oregon Landscape Contractors Association, chapters of the certification manual for the Oregon Association of Nurseries and translated master gardener materials into Spanish. Norris holds a Bachelor of Arts from Linfield College.
What Causes Yellow Spots on Meyer Lemon Trees?. The Meyer lemon (Citrus x meyeri) is a small, decorative tree known not only for its orangey-yellow fruits but for its diminutive size and lustrous green foliage. Popular in container gardening, this small tree is also useful for small backyard gardens. The fruits are …